The present invention relates to a fluid rotary apparatus widely applicable to a vacuum pump in semiconductor equipment, a compressor of a refrigerator or an air conditioner, etc.
Screw rotary machines have been used in the form of compressors or vacuum pumps in various fields utilizing vacuums, such as refrigeration, air conditioning, semiconductors, optics, foods, and medicines.
FIG. 16 shows an example of a conventional screw compressor having a male rotor 500 and a female rotor 501 arranged on two shafts parallel to each other. The rotors 500, 501 rotate in opposite directions like male and female screws meshed with each other. Tubular groove chambers in the pair of rotors defined by a casing and thread grooves of the rotors are compressed while a meshed point of the rotors is moved axially and compressed in accordance with the rotation of the rotors, so that the air is discharged.
More specifically, as shown in FIG. 17, the screw compressor includes the male rotor 500 with four convex surfaces and the female rotor 501 with six threads. When the rotors 500, 501 rotate in opposite directions, the volume of a space defined by the thread grooves and the casing is changed, so that the air is drawn, compressed, and discharged by utilizing this change of the volume. Since the air is drawn, compressed, and discharged sequentially by the thread grooves in the screw compressor of the above type, the torque changes less and the flow pulsates little, and moreover the rotary bodies are kept well balanced. Therefore, the screw compressor is advantageous in that it generates few vibrations, runs at high speeds and is of a compact structure.
In the meantime, the performance of the screw compressor is determined by the amount of internal leakage between the rotors and between the rotors and casing. The above internal leakage is detected specifically at the following points:
(1) at a point where the male rotor is meshed with the female rotor, through which the air leaks from the discharging side to the suction side; PA1 (2) at a side gap of each rotor; PA1 (3) at a gap between the outer periphery of each rotor and the inner surface of the casing, through which the air leaks from one thread groove to the other thread groove; and PA1 (4) at a path connecting adjacent thread grooves which is determined by the shape of the threads of the rotor, namely, a blow hole.
In order to avoid the leakage referred to above, the screw compressor has been processed highly accurately with the thermal expansion of each member taken into consideration and at the same time, the gap has been sealed by lubricating oil.
However, in the case where the above conventional screw rotary machine is to be applied to consumer equipment such as refrigerators, air conditioners for rooms or air conditioners for automobiles, the displacement (discharging amount per rotation) is normally 3-100 cc or so, whereby the efficiency of the compressor is greatly deteriorated due to the influences of the internal leakage as discussed above.
For all the merits of the screw-type rotary machines, i.e., low-vibration and low-noise, etc., it has been difficult to apply the screw-type rotary machines to consumer equipment, and the use of the machines has been restricted to large-size compressors, vacuum pumps and the like in the industrial field.